The present invention relates generally to fiber optic cables and, more particularly, to fiber optic drop cables.
Fiber optic cables include optical fibers that are capable of transmitting voice, video, and data signals. Fiber optic cables have advantages over electrical voice, video and data signal carriers, for example, increased data capacity. As businesses and households demand increased data capacity, fiber optic cables can eventually displace electrical voice, video, and data signal carriers. This demand will require low fiber count optical cables to be routed to end users, for example, businesses and households.
Fiber optic cables can typically be used in various applications. For example, fiber optic drop cables can be suitable for both aerial and buried cable applications. More specifically, a fiber optic drop cable can be strung between poles and/or buried in the ground before reaching the end user. Aerial and buried cable environments have unique requirements and considerations. Optical fiber drop cables should meet the unique requirements and considerations of both environments, yet still remain cost effective.
In addition to being cost effective, cables should be simple to manufacture. An example of a low fiber count optical cable manufactured in one step and having an optical fibers disposed longitudinally to the cable axis is disclosed in U.S. Pat. No. 5,115,485. An optical fiber is disposed within an electrically conductive strength member that is surrounded and embedded in an elastomeric material that forms the outer jacket. The cable also includes optical fibers embedded in the elastomeric material that forms the outer jacket. This known fiber optic cable has several disadvantages. For example, because the optical fiber is surrounded by the electrically conductive strength member, it is difficult to access the fiber. Moreover, accessing the central optical fiber can result in damage to the embedded optical fibers. Additionally, the embedded optical fibers are coupled to the elastomeric material that forms the outer jacket. Consequently, when the elastomeric outer jacket is stressed, for example, during bending, tensile and compressive stresses can be transferred to the optical fibers, thereby degrading optical performance.
Moreover, fiber optic cables that are strung between poles can carry a tensile load. An example of a fiber optic cable designed to carry a tensile load is disclosed in U.S. Pat. No. 4,422,889. This known cable is an optical fiber cable with a generally cylindrical central support member having helical grooves formed around its periphery for carrying optical fibers. During manufacture, the grooves require partial filling with a viscous filling compound, placing the optical fiber in the partially filled groove, and then filling the partially filled groove with the optical fiber with further viscous filling compound. Although this known fiber optic cable is designed to prevent the application of tensile stress to the optical fibers by allowing the fibers to sink deeper into the grooves when axially loaded, this design has several disadvantages. For example, from a manufacturing standpoint, this cable requires multiple steps at different temperatures for proper placement of optical fibers.
Optical fibers can also be twisted as they are laid in cables. An example of a fiber optic cable designed to reduce contact between a twisted optical fiber and a strength member is disclosed in U.S. Pat. No. 4,354,732. This known cable is an optical fiber cable with a helical flanked V-shaped groove. The helical flanked V-shaped groove requires a pair of flanks, over a portion of profile, which are curved convexly toward the interior of the groove. Additionally, the flanked V-groove is designed to work in concert with an optical fiber that is twisted between 3 and 10 turns per meter when inserted into the flanked groove. The fiber, which is undulated from the twisting process, is designed to rest on alternate flanked sides of the V-shaped groove and prevents an uninterrupted line of contact between the optical fiber and the strength member. Although this known fiber optic cable is designed to prevent mechanical stresses on the optical fiber, this design has several disadvantages. For example, from a manufacturing standpoint, twisting the optical fiber adds another step to the process. Additionally, twisting introduces stresses on the optical fiber that can cause undesrirable levels of optical attenuation.
One aspect of the present invention provides a fiber optic cable having at least one optical fiber component disposed within at least one retention area of a support member. The support member includes a metallic material having the retention area generally helically formed therein relative to an axis of the cable. The cable also includes an interfacial layer disposed between an outer surface of the support member and the cable jacket. The cable can include a water-blocking component, a cushioning zone adjacent the optical fiber component and/or at least one tab, extending from the support member, bendable for at least partially covering the retention area.
A second aspect of the present invention provides a fiber optic cable having at least one optical fiber component disposed within at least one retention area of a dielectric or metallic support member. The support member includes a retention area disposed substantially helically about an axis of the cable. The cable includes a cushioning zone adjacent the optical fiber component and both an interfacial layer and a water-blocking component disposed between an outer surface of the support member and the cable jacket. The cable can include at least one tab, extending from the support member, bendable for at least partially covering the retention area.
A third aspect of the present invention provides a fiber optic cable having at least one optical fiber component disposed within at least one retention area of a support member. The retention area is generally helically formed therein relative to an axis of the cable. The cable having a strain of about 1.0% or less when a 1,000 lb. tensile force is applied. The cable can include a cable jacket, cushioning zone adjacent the optical fiber component, a water-blocking component, and/or at least one tab, extending from the support member, bendable for at least partially covering the retention area.